Field of the Invention
This invention relates to a sheet conveying apparatus, an image forming apparatus, a control method of a sheet conveying apparatus, and a control program of a sheet conveying apparatus. In particular, this invention relates to a sheet conveying apparatus, an image forming apparatus, a control method of a sheet conveying apparatus, and a control program of a sheet conveying apparatus, which can detect thickness of sheets.
Description of the Related Art
When paper sheets are manually set to feed them into an image forming apparatus, a user may not comprehend the thickness of the sheets to be used. In case that image forming behavior is performed based on an incorrect configuration of the thickness of the sheets, there is the potential for the occurrence of a sheet jam, or the occurrence of the problem in transferring images to the sheets or image fixing performance. To cope with these problems, a thickness of the sheet to be conveyed by a sheet conveying apparatus is detected (sheet thickness detection), for preventing the printing failure and for improving users' convenience.
To detect sheet thickness, a sheet thickness detection method using the amount of displacement of a detection roller, when a sheet is pinched between a reference roller and the detection roller is typically used. Such a method has a problem in which the detection result varies, since the amount of displacement of the detection roller includes an amount of displacement caused by an eccentricity of the roller, in response to a rotation cycle. Because of the problem, the desired degree of detection accuracy can not be obtained.
FIG. 18 is for explanation pertaining to a conventional detection method.
In FIG. 18, the upper part shows the amount of displacement of detection roller 810, when sheet P is not pinched between reference roller 805 and detection roller 810, and the lower part shows the amount of displacement of detection roller 810, when sheet P is pinched between reference roller 805 and detection roller 810. Both when sheet P is not pinched and sheet P is pinched, the amount of displacement of the detection roller 810 periodically fluctuates, in accordance with the rotation of reference roller 805 and detection roller 810.
More specifically, where the diameter of detection roller 810 is represented by D, and the conveying velocity of sheet P is represented by S, rotation cycle C of detection roller 810 is calculated by D*π/S. When sheet P is not pinched, the amount of displacement of detection roller 810 periodically fluctuates for each rotation cycle C. The periodical fluctuation is caused by the eccentricity or the like of detection roller 810 and reference roller 805. When sheet P is pinched, the periodical fluctuation is still included in the entire amount of displacement, though the level of the amount of displacement of detection roller 810 rises by the thickness of the sheet. Hence, the detection result varies based on the detection timing.
As for such the problem, there are conventional techniques which adopt the following structures.
In the Document 1 below, the detection of the correct sheet thickness is attempted, by performing memorizing, calculating and compensating behavior for the eccentricity amount of the reference roller. More specifically, displacement signals of the detection roller within a certain period of time are recorded, after a sheet is entered between the reference roller and the detection roller. A calculation is executed between the displacement signal of the detection roller when a certain period of time which is the integral multiple of a rotation cycle of the reference roller has elapsed from when the sheet was entered, and the recorded displacement signal. Herewith, the eccentricity amount of the reference roller is corrected, for the recorded displacement signal.
According to the Document 2 below, thickness of a sheet is calculated, by using variation data during more than or equal to a rotation cycle of a roller for sheet thickness detection when the sheet is pinched and when the sheet is not pinched.
According to the Document 3 below, thickness of a sheet is calculated upon synchronizing an amount of displacement of a detection roller when a sheet is not pinched, with an amount of displacement of the detection roller when the sheet is pinched, after detection of a rotation cycle of the roller.